I have one Z9 mini September 2018 batch with firmware dated Sun Aug 12 17:43:41 CST 2018. Although the only GUI option is "Balanced", I can configure OC with web editor to any speed with the best speed being at 675 MHz and 95% fan speed for best cooling and is producing a stable 15-16kH/s hashing speed. I received three October 2018 batch minis today and the maximum OC speed in the GUI is the "balanced" setting of 500 MHz but can only be raised to 550 MHz using html editor. The miner will reject and revert to 500 MHz if any other number is attempted. Of course, the "Aug 12 17:43:41 CST 2018" firmware is no longer available on the Bitmain website which was replaced with the Aug 31, 2018 firmware which is what is on my new batch. I tried to save a config backup from the older device and restore to the new one but had no affect whatsoever. Did anyone happen to obtain the Aug 12, 2018 firmware before it was replaced and might it run as desired on the newer Z9 mini? The new Z9 minis are hashing at a consistent 12-13 kH/s at 550 MHz which is about 20% below the 15-16kH/s at 675 MHz. I may just have to live with that.